Canadian Patent 2 509 309 by Heins, entitled Water Treatment Method for Heavy Oil Production Using Calcium Sulfate Seed Slurry Evaporation, describes an evaporator based method of treating produced water from heavy oil production. Produced water is first treated in a de-oiling step to reduce oil and grease to about 20 parts per million or less. De-oiled water is introduced into an evaporator to produce a distillate and an evaporator blowdown containing concentrated residual solids. The distillate is used, optionally after further polishing, to create steam in a once-through steam generator or other boiler. The evaporator blowdown may be further treated in a crystallizer.